Paper is produced on paper making assemblies consisting of several paper processing machines. Each of these machines utilizes endless loops or webs (e.g., fabric or felt endless webs). Generally, a paper making assembly includes at least a forming stage, a press stage, a dryer stage and a winding and cutting stage. As part of paper making processes, in general, a slurry pulp mixture is disposed onto a first endless web, i.e., the forming stage felt or web. Most of the water contained in the slurry mixture is removed at this stage at which time the paper begins to take form. That is, the surface of the paper mixture itself begins to reflect the web on which it lies during this initial stage of the process.
This paper forming mixture then moves to a second stage, i.e., the press stage, which employs a second endless web. At this stage, as most of the water has been removed, the paper mixture begins to possess characteristics of finished paper. Here, too, the paper surface being formed is reflective of the surface of the web on which it lies.
Thus, it is desirable for webs in at least these initial two stages to be as smooth as possible and devoid of any imperfections or variations so that the paper, which is formed thereupon, likewise will be smooth and uniform. In this regard, the webs should be endless, instead of pieces sewn together, to make a loop. An endless web eliminates any seams either in the machine direction (i.e., the longitudinal direction in which the endless web rotates, or in the cross machine direction, i.e., the direction perpendicular or transverse to the machine direction. Such a seam would create imperfections, or at least variations in the paper, both of which are unacceptable for paper making assemblies.
Typically, the endless webs also are treated with non-contacting methods such as chemicals, mechanical and radiant energy, or by stretching or other similar methods to achieve a smooth set surface. This setting of the endless webs also must be performed in a consistent manner so as to avoid certain imperfections.
Since the webs are endless, the length of the finishing assemblies used to treat them will usually govern their overall loop length or circumferential length. This is commonly referred to as the "minimum loop length." Certain types of endless web finishing assemblies may include at least one inside treatment roll, which heats the endless web on contact, at least one inside treatment roll, which stretches the endless web, and possibly a non-contacting treatment device such as an air box (or oven), which treats the endless web without contacting it. Also, since the webs or loops are endless, the rolls and/or ovens have to be manipulated and moved out of the way so that the endless web can be loaded onto the finishing assembly and off-loaded from the finishing assembly without interference with the rolls and/or ovens and without damaging the endless web.
These endless webs are fairly large and cumbersome and it is uneconomical in terms of production time and labor costs to remove the endless webs during a treatment session. There also is always the risk of potentially damaging the web when it is being removed and turned. These webs are extremely expensive and may have to be scrapped if enough damage is incurred when unloading and turning them. Thus, it is desirable in the felt making industry to treat both the outside and inside surfaces of the endless web without having to remove or unload them, flip them inside out and reload them onto the finishing assembly again. Collectively, the manipulation of a web is commonly called "felt turning." One way to avoid this felt turning step is to employ an outside treatment device. There is a competing need to keep certain webs as small as possible, i.e., the smallest possible "minimum loop length." This is further discussed below.
Certain of these finishing assemblies include cantilevered supports for supporting one or both of the inside treatment rolls while the endless web is being loaded and unloaded. In these assemblies, the outside treatment device is usually positioned between the outside of a cantilevered support and one of the inside treatment rolls. This is so because an air box or oven set will typically be attached to the inside of the cantilevered support.
In the paper making process discussed above, it is desirable to have at least one relatively short endless web having the shortest "minimum loop length" possible. This web is usually utilized in the first stage, i.e., the forming stage. It also is desirable to treat other endless webs at varying sizes to accommodate various other stages of the paper making processes as mentioned above. Thus, it is desirable to have an endless web finishing assembly which is capable of accommodating the smallest "minimum loop length" as well as at the same time being versatile to accommodate a variety of endless web lengths and treatment processes.
However, with the introduction of an outside treatment device, as discussed above and as generally found in the prior art, the "minimum loop length" would be increased by at least the diameter or linear width of the outside treatment roll since this device is usually placed between one of the inside rolls and adjacent or outside of the cantilevered support to allow room for the air boxes or ovens. Hence, the overall "minimum loop length" is dictated by the total diameters of the inside treatment rolls, the diameter or linear width of the outside treatment device and the width of the air box set, in addition to the amount of wrap (or that portion of the endless web which contacts the rolls).
Assemblies for treating both the outside and inside of an endless web without felt turning are known. But in most of these attempts, the "minimum loop length" is necessarily increased as a result of the added equipment needed to treat the outside of the web. In certain cases, in order to maintain the "minimum loop length," oven sets or other non-contacting treatment assemblies are permanently attached to a cantilevered support or at least a bottom oven is attached and a top oven is movable. However, by keeping these ovens (or at least the bottom oven) permanently attached to a cantilevered support, it considerably reduces the amount of surface area or dwell time an outside contact treatment device can contact the endless web. This is so because to preserve the "minimum loop length," the outside contact treatment device is brought into the same area as the ovens. As such, the outside treatment device cannot be brought up high enough to increase the treatment area (i.e., wrap or dwell time).
U.S. Pat. No. 5,312,523 issued to Erickson et al., discloses a glide surface positioned between a rotatable heatable roller 2 and a rotatable roller 3. Roller 3 is movably mounted for movement toward and away from roller 2, so that it functions as a tension roller. The glide surface 4 is shown between the roller 2 and roller 3. In addition, FIG. 4 of this reference discloses a glide surface 4 and a heater box 15 where the glide surface provides only a small contact surface area. The glide surface is stationary with relation to the movement of the endless web. Thus, there is a resulting relative motion between the glide and the endless web. This relative motion may cause a less than smooth resulting web for several reasons. For instance, since the glide is stationary with respect to the moving endless web, a substantial amount of friction is created. This results in a greater potential for the endless web to bow or skew. This leads to undesirable surface, draining or other mechanical imperfections in the endless web. In addition, since there is a limited contact surface area with the glide, there is less tension control overall and less treatment area per linear foot.
Another example of an endless loop finishing assembly that provides for reducing the "minimum loop length" can be found in the aforementioned, commonly assigned U.S. patent application Ser. No. 08/924,170, the disclosure of which is hereby incorporated by reference herein. In the '170 application, there is provided a finishing assembly for treating an endless web which extends in a machine direction when loaded onto the finishing assembly. The assembly includes a cantilevered support having a generally horizontal free end including at least two cantilever beams extending in a direction generally transverse to the machine direction of the finishing assembly. The two cantilever beams define a transversely-extending open space therebetween. The finishing assembly further includes first and second inside treatment rolls for contacting the inside surface of the endless web to treat the endless web. Each inside treatment roll is arranged to be supported on the cantilevered support when in an endless web loading position. At least one of the inside treatment rolls is movable between the loading position and an endless web treatment position wherein the at least one inside treatment roll is spaced apart from the cantilevered support in a direction generally parallel to the machine direction. Also included in that aspect is a movable roll carriage device for moving the at least one inside treatment roll between the loading position and the treatment position, and an outside treatment roll for contacting the outside surface of the endless web to treat the endless web. The outside treatment roll is movable between a first position and a second position. When in the first position, the outside treatment roll is positioned in the transversely-extending open space and operative to contact the outside surface of the endless web over a predetermined contact surface area, and when in the second position, it is positioned outside of the transversely-extending open space to allow for the endless web to be loaded onto the finishing assembly.
Despite all of the effort which has been devoted to the development of a versatile endless loop finishing assembly capable of being used in various types of universal treatment applications and processes that require "minimal loop lengths," (including the positive results of the aforementioned commonly-owned and assigned invention as disclosed in the '170 application), there are unmet needs for further improvements.